Automatic coil selection of multi-receiver MR data using fast prescan data analysis

ABSTRACT

Automatic coil selection is based on determining an index gauge for a corresponding k-space data line acquired for each preselected coil during a prescan. Reliance on manual coil selection and markers is eliminated by adaptively determining the coils of an MR system that produce a preferred sensitivity to a desired field-of-view (FOV). The fast scan data is used to determine those coils most sensitive to the FOV and reject coil(s) least sensitive. Using only data acquired with the most sensitive coils, SNR is increased and unwanted artifacts are reduced in the final data acquisition and image reconstruction. Through automatic and adaptive selection/deselection, the invention reduces the susceptibility to human error, and therefore results in higher quality images.

BACKGROUND OF INVENTION

[0001] The present invention relates generally to MR data acquisitionand, more particularly, to a method and system for imaging with adaptiveautomated coil selection of a multi-coil imaging receiver assembly in amedical imaging device.

[0002] Diagnostic imaging devices, such as magnetic resonance (MR)scanners, can acquire imaging data using a series of receivers. Further,improved imaging devices can employ a coil assembly of phased arraycoils to acquire the imaging data over a desired imaging field-of-view(FOV). Phased array coils are often used because they yield a highersignal-to-noise ratio (SNR) and increased spatial coverage over thedesired FOV. In these known imaging systems, imaging data acquired fromeach phased array coil is combined to form a final diagnostic image.Despite the implementation of phased array coils, reconstructing animage from the combination of the imaging data from all, or too many, ofthe phased array coils can produce ghosting in the final image fromunwanted noise and artifacts.

[0003] Typically, these unwanted artifacts result from the acquisitionof data from a phased array coil assembly that dimensionally exceeds thedesired FOV of a subject, i.e., a medical patient. For example, in aknown MR system that utilizes a coil assembly with six phased arraycoils, it is customary to utilize four of the six coils during a spinalimaging examination. However, in some spinal exams, the imaging FOV canbe covered with only two or three coils to acquire sufficient data toproduce a complete image. As a result of using the additional andunnecessary coils, noise and artifacts insensitive to the selected FOVare often included in the final image and result in undesirable ghostingin the final image. To reduce the noise and unwanted artifacts, it isdesirable to use only those coils that are sensitive to the desired FOV.

[0004] Known systems seek to maintain sensitivity of the FOV bypermitting manual selection of coils based upon patient positioning andother positioning tools prior the imaging session. Essentially, in theseknown diagnostic systems an MR operator or technician manually deselectscoils so that these deselected coils do not acquire data during theimaging scan or, alternatively, specifically excludes data fromarbitrary coils that are acquired during scanning from final imagereconstruction on a trial and error basis. To properly deselect theappropriate coils, the operator must know exactly which coils todeactivate prior to the diagnostic scan, which is a difficult and timeconsuming task, and often requires guess work. The task of properlyselecting the coils is exaggerated by the fact that the patient andpatient table can frequently change positions during an imaging session.Further, deselection of the proper coils is a cumbersome task and oneprone to human error that could result in requiring a total rescan. Torequire the operator to repeatedly deselect coils with each new patientand/or table position only increases the difficulty of deselecting theappropriate coils. Further, with multi-slice imaging techniques it wouldbe necessary for the operator to deselect different coils during theimaging session—a daunting task in operator-based selection.

[0005] Attempts to automate coil selection have, in fact, not been madecompletely automatic. For example, in one approach the coils areselected only after requiring a system operator to furnish the scannerwith 2-3 parameters that are based on the positioning of a landmark, orreference mark, placed on the subject at some known distance fromisocenter. Such a system requires accurate placement of the landmark, orrequires a measurement of the distance between the landmark andisocenter, and that measurement must be input into the system togetherwith a dimension of the field-of-view between a pair of boundary limits,relative to the isocenter. Further, after the operator inputs thenecessary parameters, some such known systems utilize conventional logiccircuits together with a lookup table to select or deselect certaincoils. Other known systems use a pilot scan, or prescan, to acquireparameters of a selected slice or imaging sequence and compare theseproperties to properties of the coil array that are stored in a lookuptable. Not only do these systems rely on static data, they are subjectto human error and/or require additional hardware configurations, and inthe case of using markers, the images have to either be manually griddedor additional time and resources are expended on automatic gridding ifthe marker is machine identifiable. Examples of two coil selectionsystems include U.S. Pat. Nos. 5,138,260 and 6,134,465. Although suchsystems have functioned adequately, it would be desirable andadvancement in the art, to design a fully automated system that does notrely on manual intervention, lookup table, and/or landmarks.

[0006] It would therefore be desirable to design a method and system tofully automate coil selection of an imaging device, or data fromspecific coils, to increase FOV sensitivity and clarity formulti-channel phased array imaging. It would similarly be desirable todesign a method and system to determine phased array coil positionsadaptively using an on-the-fly index gauge determination that is notdependent on a status lookup table, thereby facilitating selection ofcoils for image reconstruction with reduced artifacts.

SUMMARY OF INVENTION

[0007] This invention includes a method and system that is an adaptiveand full-automated coil selection technique that overcomes theaforementioned drawbacks. The present invention facilitates imagereconstruction with an increased signal-to-noise ratio and reducedartifact presence without manual selection of specific coils, withoutthe use of reference marks and landmarks, and without using look-uptables. Through automatic selection and/or deselection of coils, thepresent invention discriminates between coils in an imagingfield-of-view (FOV) based on an index gauge. Using imaging data fromthose coils with the best sensitivity within the FOV enablesreconstruction of a final image with reduced noise and reduced artifactsfrom the image. The present invention implements automatic selection ordeselection of coils based on an adaptive and dynamic analysis ratherthan reliance on manual selection, operator inputs, and/or landmarkplacement processes often prone to human error and requiring additionalhardware.

[0008] In one embodiment of the present invention, preliminary scanningdata is acquired during an initial fast scan. With a fast scan, alimited number of k-space data lines are acquired and sampled. Byemploying a fast scan, the present invention allows for a preliminaryanalysis to be completed to determine those phased array coils mostsensitive to a FOV before acquiring a full set of imaging data.Typically, a fast scan or preliminary scan requires less time tocomplete than a full reconstruction imaging scan. After the preliminaryimaging data is acquired during the fast scan, the imaging data isanalyzed and evaluated to determine which coils to activate during afull reconstruction imaging session. Analyzing and evaluating thepreliminary scan to determine which coils to activate or deactivateduring a full imaging session may be carried by adaptively determiningan index gauge for at least one k-space data line acquired for eachcoil, comparing the index gauge on-the-fly, and then automaticallyselecting or deselecting a number of MR coils to activate for image dataacquisition based on the comparison of the dynamically determined indexgauge.

[0009] In accordance with one aspect of the present invention, a methodto automatically select/deselect coils, for image reconstruction, usingprescan image data of an MRI device having a number of coils isprovided. The method includes the step of initializing a fast scan toacquire k-space data sets via a number of phased array coils. The numberof k-space data sets includes at least one k-space data line for each ofa plurality of MR coils. In evaluating the k-space data, an index gaugeis adaptively determined for at least one k-space data line acquired foreach coil. A threshold value is dynamically found for a comparison ofthe index gauges. In this manner, a number of MR coils can beautomatically selected, or deselected, based on the index gaugecomparison.

[0010] In a preferred embodiment, the index gauge can include anintensity value extracted from the k-space data. In this case, theintensity values are then arranged into an intensity profile thatenables identification and selection of a number of phased array coilsto activate for final imaging data acquisition. After the coils to beactivated have been selected, or the coils to be inactive aredeselected, full image data can be acquired to reconstruct an image withincreased SNR.

[0011] In accordance with another aspect of the invention, a computerprogram is disclosed that includes instructions to cause a computerprogram to acquire and analyze prescan data acquired from activating anumber of phased array coils during a preliminary MR scan, and thenextract a relative intensity of the data for each coil. Based on therelative intensity of each coil, a number of phased array coils isselected, or deselected, for activation to acquire data during areconstruction imaging scan. Accordingly, the selection or deselectionof the coils is made dynamically and without operator input or markers.

[0012] In accordance with yet another aspect of the present invention,an MRI apparatus is disclosed having a magnetic resonance imaging systemhaving a plurality of gradient coils positioned about the bore of amagnet to impress a polarizing magnetic field and an RF transceiversystem. The MRI apparatus further includes an RF switch controlled by apulse module to transmit RF signals to a phased array coil assembly toacquire the MR images. The MRI apparatus also includes a computerprogrammed to initialize a fast MR scan using a plurality of coils inthe phased array coil assembly and acquire fast scan imaging data of animage FOV. The fast scan imaging data includes at least one k-space lineof data for each of the plurality of coils in the phased array coilassembly. The computer is also programmed to determine a relativeposition of each of the plurality of coils with respect to the desiredFOV based only on the at least one k-space line of data. The computercan then select and initialize only a number of the plurality of coilsfor image acquisition and reconstruction based on the relative positionsof each coil in order to optimize SNR in the desired FOV.

[0013] Various other features, objects and advantages of the presentinvention will be made apparent from the following detailed descriptionand the drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The drawings illustrate one preferred embodiment presentlycontemplated for carrying out the invention. In the drawings:

[0015]FIG. 1 is a schematic block diagram of an MR imaging system foruse with the present invention.

[0016]FIG. 2 is a schematic representation of a multi-coil MRI systemfor use with the present invention.

[0017] FIGS. 3-5 taken together show a flowchart for selecting coils ofan MRI system in accordance with the present invention.

[0018]FIG. 6 is a flowchart to facilitate automatic coil selection inaccordance with the present invention.

DETAILED DESCRIPTION

[0019] Referring to FIG. 1, the major components of a preferred magneticresonance imaging (MRI) system 10 incorporating the present inventionare shown. The operation of the system is controlled from an operatorconsole 12 which includes a keyboard or other input device 13, a controlpanel 14, and a display 16. The console 12 communicates through a link18 with a separate computer system 20 that enables an operator tocontrol the production and display of images on the screen 16. Thecomputer system 20 includes a number of modules which communicate witheach other through a backplane 20 a. These include an image processormodule 22, a CPU module 24 and a memory module 26, known in the art as aframe buffer for storing image data arrays. The computer system 20 islinked to disk storage 28 and tape drive 30 for storage of image dataand programs, and communicates with a separate system control 32 througha high speed serial link 34. The input device 13 can include a mouse,joystick, keyboard, track ball, touch activated screen, light wand,voice control, or any similar or equivalent input device, and may beused for interactive geometry prescription.

[0020] The system control 32 includes a set of modules connectedtogether by a backplane 32 a. These include a CPU module 36 and a pulsegenerator module 38 which connects to the operator console 12 through aserial link 40. It is through link 40 that the system control 32receives commands from the operator to indicate the scan sequence thatis to be performed. The pulse generator module 38 operates the systemcomponents to carry out the desired scan sequence and produces datawhich indicates the timing, strength and shape of the RF pulsesproduced, and the timing and length of the data acquisition window. Thepulse generator module 38 connects to a set of gradient amplifiers 42,to indicate the timing and shape of the gradient pulses that areproduced during the scan. The pulse generator module 38 can also receivepatient data from a physiological acquisition controller 44 thatreceives signals from a number of different sensors connected to thepatient, such as ECG signals from electrodes attached to the patient.And finally, the pulse generator module 38 connects to a scan roominterface circuit 46 which receives signals from various sensorsassociated with the condition of the patient and the magnet system. Itis also through the scan room interface circuit 46 that a patientpositioning system 48 receives commands to move the patient to thedesired position for the scan.

[0021] The gradient waveforms produced by the pulse generator module 38are applied to the gradient amplifier system 42 having G_(x), G_(y), andG_(z) amplifiers. Each gradient amplifier excites a correspondingphysical gradient coil in a gradient coil assembly generally designated50 to produce the magnetic field gradients used for spatially encodingacquired signals. The gradient coil assembly 50 forms part of a magnetassembly 52 which includes a polarizing magnet 54 and a whole-body RFcoil 56, which can include a phased array coil assembly. A transceivermodule 58 in the system control 32 produces pulses which are amplifiedby an RF amplifier 60 and coupled to the RF coil 56 by atransmit/receive switch 62. The resulting signals emitted by the excitednuclei in the patient may be sensed by the same RF coil 56 and coupledthrough the transmit/receive switch 62 to a preamplifier 64. Theamplified MR signals are demodulated, filtered, and digitized in thereceiver section of the transceiver 58. The transmit/receive switch 62is controlled by a signal from the pulse generator module 38 toelectrically connect the RF amplifier 60 to the coil 56 during thetransmit mode and to connect the preamplifier 64 to the coil 56 duringthe receive mode. The transmit/receive switch 62 can also enable aseparate RF coil (for example, a surface coil) to be used in either thetransmit or receive mode.

[0022] The MR signals picked up by the RF coil 56 are digitized by thetransceiver module 58 and transferred to a memory module 66 in thesystem control 32. A scan is complete when an array of raw k-space datahas been acquired in the memory module 66. This raw k-space data isrearranged into separate k-space data arrays for each image to bereconstructed, and each of these is input to an array processor 68 whichoperates to Fourier transform the data into an array of image data. Thisimage data is conveyed through the serial link 34 to the computer system20 where it is stored in memory, such as disk storage 28. In response tocommands received from the operator console 12, this image data may bearchived in long term storage, such as on the tape drive 30, or it maybe further processed by the image processor 22 and conveyed to theoperator console 12 and presented on the display 16.

[0023] Shown in FIG. 2 is a representation of an imaging area resultingfrom implementation of a multi-coil MRI system, such as that generallyshown in FIG. 1. For illustration purposes, the imaging area 80 resultsfrom a four-coil selected MRI device. One of ordinary skill in the art,however, will appreciate that the invention set forth herein isapplicable to any multi-coil imaging device. The imaging area 80 shownin FIG. 2 includes four separate yet overlapping coil coverage areas 82,84, 86 and 88. Each coil coverage area 82-88 is dimensionally equivalentand represents an equally proportioned data acquisition region of thepatient 90. The combination of the coil coverage areas 82-88 results ina sum coil coverage area 81. Within the sum coil coverage area 81 is adesired image field-of-view (FOV) 92, that can span across severalindividual coil coverage areas 82-88. The image FOV 92 can bedimensionally identical to the sum total of the coil coverage areas82-88, but, in many situations, such as shown in FIG. 2, the image FOVmay be less than the sum of the coil coverage areas 82-88. When the sumcoil coverage area 81 exceeds the image FOV 92, one or more of the coilsof the MRI system often acquire imaging data outside the desired FOV 92.Further, as shown in FIG. 2, since portions of coil coverage areas 82and 88 lie outside the desired FOV 92, imaging data from these areas mayhave undesirable effects, such as poor field homogeneity, severe eddycurrents, and low SNR.

[0024] To reduce noise in a final reconstructed MR image and to helpeliminate unwanted artifacts, a technique to fully automate coilselection is disclosed. To produce an artifact reduced reconstructedimage with increased SNR, the system includes a coil receiver assemblyhaving a series of phased array coils, such as those found on a GE 1.5TSigna® System. As indicated previously, the MR imaging signals detectedby the receiver coil assembly are digitized and transferred to a memorylocation within the MRI system of FIG. 1. Data is organized in setscorresponding to each coil from which it was received. Using the storedMR image data, a computer program having a set of instructions causes acomputer to determine an index gauge for each MR image data set. Thesystem provides for the computer to determine from which phased arraycoil a particular image data set was acquired. By recognizing from whichcoil a particular image data set pertains, the computer is able toadaptively and dynamically select or deselect those coils and theircorresponding images that should be used for final image reconstructionbased on the index gauge. It is noted, depending on context, one mayeither “select” a subset of coils, or “deselect” coil(s). Since the endresult is the same, which term is used is irrelevant. Therefore, selectand deselect are used herein interchangeably and are hereby defined tohave substantially the same meaning.

[0025] An index gauge is constructed to sort out all the active coilelements corresponding to a distance to the selected FOV. As opposed toattempting to determine coil positions explicitly, either manually orusing some positional markers for coil selection, the present inventioncapitalizes on a theory that the closer the coil element is concentratedwithin the selected FOV, the higher sensitivity it will have to the sameregion of interest. Therefore, in one embodiment, a convenient indexgauge is selected as the total intensity of each image, which will befurther explained hereinafter. In general, the present invention isbased on dynamically extracting relative sensitivity information foreach coil from the individual images produced, or from the raw data in arescan, to differentiate data on-the-fly. Conversely, the prior artrelies on coil selection that is dependent on patient and a landmarkpositioning, obtaining and inputting certain parameters by the operatorsprior to imaging, and/or using coil markers and a prescan image to guidecoil selection with predetermined parameters or properties stored in alookup table.

[0026] Preferably, in one embodiment the disclosed technique achievesfully automated coil selection by using information contained in a setof intermediate images. These intermediate images are the individualcomponent images from each separate coil before their combination into afinal image. If desired, the information derived from these intermediateimages can be combined with specific coil geometries and physicalconfigurations. However, it is contemplated that this additional stepwould be optional, and the invention is not so limited. The intermediateimage from the i-th coil is given as:

I _(i)(x,y)=S _(i)(x,y)M(x,y);   (Eqn. 1)

[0027] where I_(i) (x,y) represents the intermediate image from the i-thcoil, S_(i) (x,y) represents the spatial sensitivity in the i-th coil inthe FOV, and M(x,y) represents the spin density, including the properspin relaxation, of the object to be scanned within the selected FOV.

[0028] In one embodiment of the invention, the coils to be included infinal image reconstruction are selected or deselected based on therelative integrated image intensity of each MR image detected by thephased array coil assembly. With this approach, a convenient index gauge(G_(i)) is the total intensity of each image, which is proportional tothe integrated coil sensitivity over the FOV under the approximation ofa constant spin density, as given as: $\begin{matrix}{{G_{i} = {\sum\limits_{({x,y})}\left| {{S_{i}\left( {x,y} \right)}{M\left( {x,y} \right)}} \middle| {\approx {M\quad o\sum\limits_{({x,y})}}} \middle| {S_{i}\left( {x,y} \right)} \right|}},} & \left( {{Eqn}.\quad 2} \right)\end{matrix}$

[0029] where G_(i) is the index gauge and M_(o) is the approximateconstant spin density. The summation is over the spatial pixels in theselected FOV. Based on the image intensity of the MR images, theinvention automatically deselects the coil(s) producing images with theleast desirable image intensity for final image reconstruction.

[0030] To determine which coils and their respective images to excludefrom final imaging, the present invention contemplates the exclusion ofimages having an intensity less than an intensity threshold value. Thethreshold value can depend on the coil geometry and the particularimaging parameters selected by the operator and will be describedfurther with reference to FIG. 3. Generally though, the intensitythreshold value is the product of a maximum mean value and the number ofreceiver coils preselected. Preferably, the intensity threshold value isdetermined on-the-fly based on the index gauge for each of the coils. Inthis manner, the coils are compared to one another dynamically insteadof some predetermined parameter. It is noted that with constant spindensity (M(x,y)), the image intensity for each detected MR image isequal to the integrated coil sensitivity over the chosen FOV, whichshould decrease as the distance between the phased array coil and theFOV increases. Further, in the practical case where there is a presenceof spatial variation in the spin density, the relationship between imageintensity and coil distance from the selected FOV holds because thesensitivity values of different phased array coils are weighted by thesame spin density value or profile.

[0031] The present invention further contemplates an alternativeembodiment for determining which images to include and/or exclude fromfinal image reconstruction. This alternative embodiment, as set forthbelow, may be used in place of or in conjunction with the techniqueheretofore discussed. To enable adaptive selection of phased array coilsand the data for reconstruction, the technique includes projecting theintensity of each MR image onto a major axis of the receiver coilassembly. This projection of image intensity onto a map of the receivercoil assembly allows the computer to determine those phased array coilsthat acquired the most pronounced images. Those pronounced images, i.e.,those images with the highest intensity, reveal and normally correspondto those phased array coils most sensitive to the selected FOV.

[0032] Rather than determining phased array coil position from anintensity profile fit, the computer may be programmed to alternativelydetermine a center of mass of the images based on image intensity. ThoseMR images with concentrations near the center of mass indicate whichphased array coils are most significantly sensitive to the desired FOV.In a further embodiment, the computer may be programmed to find the peaklocation of the intensity profile along the major axis of the phasedarray coils. The peak image intensity location reveals which coils aremost sensitive and are within the selected FOV. In those situationswhere the intensity profile, or alternatively the center of mass or peakimage intensity position, cannot be reliably determined because a phasedarray coil lies outside the selected FOV, the phased array coil positionmay be determined from the positioning of the phased array coils locatedwithin the FOV. Determination of a coil position outside the FOV ispossible because the relative coil distance and the relative coilposition for a given phased array coil is fixed. Once the coil positionis determined relative to the selected imaging FOV, the inventionautomatically selects which coils are to be included and thus, thosecoils to be excluded from final image reconstruction.

[0033] The index gauge (G_(i)) calculation described with reference toEqn. 2 is just one example for finding an index gauge, such as the totalintensity of each image. Other index gauges are contemplated and withinthe scope of the present invention. Another example of a index gauge canbe designed without assuming a constant spin density such as:$\begin{matrix}{G_{i} = {{\sum\limits_{({x,y})}\left( \left| {I_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {I_{i}\left( {x,y} \right)} \right| \right)} = {\sum\limits_{({x,y})}\left( \left| {S_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {S_{i}\left( {x,y} \right)} \right| \right)}}} & \left( {{Eqn}.\quad 3} \right)\end{matrix}$

[0034] where S_(i)(x,y) is a spatial sensitivity of an i-th MR coil ofan N-coil phased coil array, I_(i)(x,y) is a total intensity obtainedfrom central k-space data for each MR coil, and wherein the summation isover all spatial pixels in a desired FOV. It is also noted that theindex gauge can be determined before image reconstruction because thetotal intensity is within the central portion of the k-space data. Oncethe intermediate images are sorted according to their respective indexgauge, inclusion into the final image can be based on either setting athreshold to the gauge index, or on selecting a number of coils for agiven protocol.

[0035] Referring to FIGS. 3-5, the present invention includes analgorithm 100 for automatically and dynamically selecting coils and/ordata for image reconstruction that is adaptive to many configurationswithout using landmark hardware and lookup tables with predefined datatherein. The invention further contemplates a computer program having aset of instructions that when executed causes one or more computers tocarry out the steps of the algorithm, or method, as will also bedisclosed with reference to FIGS. 3-5. The specific embodiment describedwith reference to FIGS. 3-5 is one in which complete MR data is acquiredfor each coil preselected. That is, as an example, if a six elementphased array coil is used to image the spine, typically only the middlefour elements are used, and it is those four elements that arepreselected. In one particular embodiment, complete image data isacquired for all the coil elements, including the coil elements that maynot be as sensitive to the selected FOV as the others. In this case, ifdata from the coil elements that are not as sensitive to the selectedFOV were used in final image reconstruction, they would contribute tothe introduction of additional noise and render the final image prone toartifacts since these coils may be sensitive to spatial regions beyondthe design volume of the scanner system. As previously alluded to, inone embodiment, after complete data acquisition from all preselectedcoil elements, the data can be processed into individual images beforereconstruction into a single image. With the coil selection algorithm ofthis embodiment, the image from the least sensitive coil element(s) isrejected automatically based on the index gauge. In another embodiment,a fast prescan is conducted to acquire and analyze only central k-spacedata. In this case, the coil(s) that produce the least desirable indexgauge are eliminated from acquiring complete k-space data for imagereconstruction. Although the description of the algorithm shown in FIGS.3-5 is primarily focused on the former, one skilled in the art willreadily recognize an implementation of the latter taken together withthe detailed description of the invention.

[0036] Referring first to FIG. 3, the aforementioned process 100 beginsat 102 with the acquisition of MR image data 104 or a fast prescan toacquire the raw central k-space data, as previously outlined. Afteracquisition of the MR images at 104, the operator of the MRI system maychoose whether to implement the automatic coil selection technique andsystem of the present invention at 106. If the operator chooses not toimplement the automatic coil selection technique 106, 108, MR imagingdata from each phased array coil of the coil assembly is accumulated at110 and used to reconstruct a final image at 112. However, if theoperator elects to implement the automatic coil selection system 106,114, then an image intensity value is determined at 116 for eachacquired data set. This option would be provided earlier if the prescanembodiment is implemented.

[0037] Beginning at 118, the image intensity values determined at 116are arranged to correspond to a particular receiver coil of the coilassembly whether acquired with the fast prescan or if full image data isacquired. Organizing the image intensity values in this manner allowsthe system to determine a mean intensity value for each receiver coil.As the image intensity values are organized, the intensity valuesassociated with a particular receiver are stored in bulk access memory(BAM) of the MRI system. It is then determined at 120 if the imageintensity values for the images associated with each receiver coil ofthe coil assembly have been stored in memory of the MRI system. If allthe image intensity values associated with each receiver coil have notbeen received 120, 122, the process returns to step 116 to determine andstore in memory the image intensity values for any remaining receivercoils. Once the image intensity values associated with the last receiverhave been stored in memory and verified at 124, a mean value isdetermined and stored at 126 for each receiver coil based on the imageintensity values associated with each particular receiver coil. Usingthe mean values determined at 126 for each receiver coil, a maximum ortotal mean value is determined at 128. The maximum or total mean valuedetermined at 128, will be utilized in establishing a threshold valuethat must be exceeded before those images acquired by a particular coilare included in final image reconstruction.

[0038] Continuing to FIG. 4, the present invention affords the operatorseveral options to automatically select phased array coils and theircorresponding MR images for final image reconstruction. However, theoperator is not required to input any parameters to execute theautomated coil/data selection. The options merely allow the operator toopt-out of a fully automated selection. The operator can opt to asemi-automatic selection at 130 where the operator selects a desirednumber of receiver coils to be used for data acquisition or final imagereconstruction. If the operator chooses to allow a fully automatedselection of coil data to use, or select the number of coils 130, 132,then the number of coils used for image reconstruction will be basedsolely on the technique of the present invention after determining adesired FOV size at 134. The technique provides an initial division ofthe coils with a determination of a minimum FOV 136, an intermediate FOV140, and a maximum FOV 144. As an example, in a typical MRI system, eachphased array coil is 120 mm in length. Therefore, in a preferredembodiment, a minimum FOV size 136 corresponds to an FOV ranging from 0to 180 mm in length. Further, in response to a finding of minimum FOVsize 136, the technique automatically concludes at 138 that MR imagedata acquisition from two phased array coils are adequate to realize theminimum FOV. The present invention further contemplates an intermediatesized FOV 140 corresponding to an FOV ranging in 181-450 mm andrequiring MR image data acquisition from three phased array coils 142 tofill an intermediate sized FOV. Additionally, a maximum FOV 144 may bedetermined and includes any FOV larger than 450 mm. To achieve a maximumFOV range of greater than or equal to 450, MR image data acquisitionfrom four phased array coils 146 are necessary.

[0039] As indicated previously, the present invention contemplatesoperator intervention to manually choose the number of phased arraycoils to be used for final image reconstruction 130, 133. Under thisoption, the operator may select any number of coils ranging from one tothe total number of coils in the MRI system 135, but not specific coils.After receiving the operator's number of receiver coils selection at135, the technique determines if the number of coils selected is morethan a single coil at 148. If not 150, the process proceeds to determineFOV size at 134 as previously discussed. If the operator identifies onlyone coil to be used in final image acquisition and reconstruction at135, or does not select any coils, the process ignores such an invalidinput and selects at least two coils for final image reconstruction. Thesystem may provide operator feedback with a notice of the invalid inputand an opportunity to correct the input. The steps for initiallydetermining the number of coils to use during final image dataacquisition and reconstruction for an operator selection of one, or noselection at all, are described with reference to steps 134-146 aspreviously discussed.

[0040] If the operator selects more than one receiver coil 148-152, thepresent invention determines at 154 if the number of coils selected isless than a maximum number of coils allowed for the acquisition, whichis four as is shown in FIG. 2. If the number selected is not less thanthe maximum 156, a register index and/or counter is initialized to avalue of zero at 158. Initializing the register index and/or counter toa value of zero at 158 assures that each receiver mean value stored inmemory at 126 is properly evaluated. After the register index isinitialized at 158, the receiver mean value stored in a first registerposition is called and compared at 160 to an intensity threshold value.The intensity threshold value represents a basis for determining whichcoils to exclude from image reconstruction.

[0041] Preferably, the intensity threshold value is the product of themaximum mean determined at 128, FIG. 3, and the number of receiver coilsselected at 135. Moreover, the product is divided by 100 therebyyielding a percentage value. Empirical data suggests that an intensitythreshold value of approximately 60-65% has been sufficient to excludeimages from those coils that are least sensitive to the desired FOV. At160, the receiver mean value for a first receiver mean is compared tothe intensity threshold value. If the first receiver mean value isgreater than or equal to the intensity threshold value 161, a value ofone is assigned to the first receiver at 162. If the receiver mean valueis less than the intensity threshold value 164, the register index isincremented by one at 166 thereby leaving a value of zero for the firstphased array coil.

[0042] At 168, the method and/or computer program compares the currentregistry index with the total number of coils selected at 135. If thecurrent registry index does not exceed the number of coils selected 170,the technique returns to step 160 and compares the receiver mean valueof the next phased array coil to the intensity threshold value. Stepsand/or acts 160-170 continue until each receiver mean value has beencompared to the intensity threshold value and a proper register value,i.e., one or zero, has been appropriately assigned. Once each receivermean value has been evaluated, the method and/or computer programproceeds along execution path C to step 190 of FIG. 5 as will bediscussed shortly.

[0043] Referring back to step 154, FIG. 4, if the number of selectedcoils are, in fact, less than a maximum, in this case four, the methodand/or computer program continues at 172. In a situation wherein thenumber of coils selected is greater than one but less than the maximum,the process will select and use the “best” coils for image dataacquisition and reconstruction. That is, an operator selection of threecoils for image reconstruction will be recognized by the process, butsuch a selection of three coils merely represents the total number ofcoils to be used as part of image reconstruction and not the specificthree coils to be used. Determining the “best” coils to use 138, 142,146 is done generally using the index gauge, and more particularly,using one of the techniques previously described, or any other techniqueto perform the task without additional operator input and landmarkers,and/or lookup tables.

[0044] Under all circumstances, except for a selection of a number ofreceiver coils in excess of the maximum, each receiver mean value willbe compared to an internal, pre-selected threshold value determined at174. This internal threshold value operates as an additional limiter ofMR images or raw data acquisition to be included in the finalreconstruction. For example, the process may recognize an internalthreshold value of 45%. With this threshold value, each receiver meanvalue will be compared to this internal threshold value and eachreceiver mean value will be appropriately ranked. If the method and/orcomputer program automatically determines that three receiver coils areneeded for the selected FOV or the operator identifies three as thedesired number of coils to use, the “top” three receiver means will beconsidered for image reconstruction based on the internal thresholdvalue.

[0045] Likewise, the internal threshold value operates to exclude imagesfrom receiver coils that otherwise may have been used for imagereconstruction. For instance, an operator may request at 135 that tworeceiver coils be used for image reconstruction, however, only one ofthe receiver coils may have a receiver mean value that exceeds theinternal threshold value. As a result, only data acquired from the onereceiver coil will be used for final image reconstruction despite theoperator's request that two receiver coils be considered.

[0046] After those coils having a receiver mean exceeding the internalthreshold limit are determined at 174, a first registry location isaccessed and set to zero at 176, FIG. 5. The first receiver meancorresponding to the first registry location is then retrieved andcompared to an intensity index threshold value at 178. The intensityindex threshold value may depend on hardware parameters andspecifications. However, empirical data suggests that an intensity indexthreshold of approximately 60-65% of the total receiver mean can resultin a final reconstructed image absent significant ghosting and noise. Ifthe receiver mean associated with the first registry location does notexceed the intensity index at 180, then a value of zero is assigned tothe receiving coil associated with that particular receiver mean 182,and that coil/data is rejected. If the receiver mean is greater than orequal to the intensity index 178, 184, a registry value of one isassigned to the receiver coil of the coil assembly at 186, and thecorresponding coil/data is considered acceptable.

[0047] Once a value of zero or one has been appropriately designated tothe current receiver coil, the method and/or computer program proceedsat 188 to the registry location corresponding to the next receiver coilof the coil assembly. At 190, the method and/or computer programdetermines if any additional receiver mean values need to be compared tothe intensity index threshold. If so 192, the method and/or computerprogram loops back to step 178 and determines if the new currentreceiver mean exceeds the intensity index threshold and proceeds throughsteps 180-188 accordingly.

[0048] Once the last receiver mean has been compared and no additionalreceiver mean values are available 190, 194, the computer program and/ormethod continues to step 196 to select the MR data needed for imagereconstruction. The selection of data for image reconstruction will bediscussed in further detail with reference to FIG. 6. Once the selectionof data and the final image is complete, the current method and/orcomputer program terminates at 198.

[0049] Referring now to FIG. 6, a flow chart representing the steps of amethod and/or acts of a computer program in accordance with the presentinvention is shown to select data or select the coils for MR imagereconstruction based on the registry values assigned to the respectivecoils of the coil assembly in accordance with the steps and/or acts ofFIGS. 3-5. The method and/or computer program to select data or selectthe coils for image reconstruction 200 begins at 210 with the accessingof registry information at 220. The registry values are retrieved frommemory and analyzed one at a time to determine which coils should havetheir respective MR images, or raw data, used for image reconstruction.A first registry value is retrieved and compared at 230 to a registryindex value of one. If the registry index has a value of one and thefirst accessed registry value also has a value one, the processcontinues at 232 and selects the receiver coil corresponding to thefirst registry value for final image data acquisition and reconstructionat 234. Conversely, however, if the registry value for the firstreceiver coil does not equal a registry index value of one 230, 236,then the process continues to step 238 without the receiver coilassociated with the first registry value being included in the finalimage acquisition and reconstruction or in deselecting that coil forfinal image data acquisition. At 238, the process increments to the nextregistry location corresponding to the next receiver coil of the coilassembly. At 240, a determination is made if registry values for anyadditional receiver coils are available. If so 242, the process beginsanew at step 220 for the new registry value. If no additional registryvalues need to be analyzed 244, selection of the receiver coils, or datato be used for final image acquisition and reconstruction terminates at246 with each receiver coil having MR imaging data exceeding one or moreintensity index thresholds included in the final image reconstruction,or selecting only those coils with prescan data that exceeds thesespecifications are activated for complete data acquisition.

[0050] Therefore, the present invention contemplates an adaptive methodto automatically select MR data for image reconstruction that includesacquiring an image data set from each of a plurality of receiver coilsand then determining an index gauge for each image data set. The indexgauge is a representation of a spatial relationship between a givenreceiver coil and a desired FOV. The method next includes comparing theindex gauges, and removing any image data set having an index gaugedemonstrating a spatial relationship between the given receiver coil andthe desired FOV that is less than optimal based on the comparison. Theprocess also includes reconstructing an image from the remaining imagingdata sets.

[0051] In another embodiment of the present invention, a method ofautomatically determining a subset of acquired data from a field-of-viewof a receiver assembly that has a number of coils therein is disclosed.This method includes acquiring a number of images from a plurality ofcoils of an FOV and determining an image intensity for each of thenumber of images. The process also includes projecting the imageintensity of each image onto a virtual access of the plurality of coilsto create an intensity profile map. A subset of images is then selectedbased on the intensity profile map to reconstruct an image with reducedartifacts.

[0052] In accordance with yet another embodiment of the presentinvention, an MR imaging apparatus to acquire scanned images isprovided. The MR imaging system further includes an RF transceiversystem and an RF switch controlled by a pulse module to transmit RFsignals to an RF coil assembly to acquire MR images. Receiver assemblieshaving a number of phased array coils are often used in magneticresonance imaging systems. The coils are typically positioned about thebore of a polarizing magnet to impress a polarizing magnetic field. Theapparatus includes a computer programmed to acquire an MR image fromeach coil of a multi-coil RF coil assembly across an image FOV anddetermining an intensity value for each MR image. The computer alsodetermines an intensity value for each MR image and differentiates theMR images acquired from each coil based on the intensity values in orderto discard any MR image having excess data acquired outside the imageFOV. A final image can then be reconstructed with reduced artifacts bycombining the remaining MR images.

[0053] Another embodiment of the invention includes a computer programhaving a set of instructions such that when executed by a computercauses the computer to acquire a set of imaging data includes a numberof data frames, determine an intensity value for each data frame, anddetermine an intensity index from each intensity value. The program thenforms a reconstruction data set that only includes the data frameshaving an intensity value exceeding the intensity index andreconstruction image from the reconstruction data that eliminates atleast one data set being the least sensitive to the FOV.

[0054] An MR scanner is also disclosed that includes a means foracquiring an image data set from each of a plurality of receiver coilsand a means for determining an index gauge for each image data set,wherein the index gauge represents a spatial relationship between agiven coil receiver and a desired FOV. The MR scanner also has a meansfor removing any image data set having an index gauge demonstrating aspatial relationship between the given receiver coil and the desired FOVthat is less than optimal based on the comparison. The scanner alsoincludes a means for reconstructing an image from the remaining imagingdata sets.

[0055] The present invention also contemplates a method to automaticallyisolate, for image reconstruction, scanned images of an MRI devicehaving a number of phased array coils. The method includes the steps ofacquiring, via the phased array coils, a number of imaging data framesincluding a number of k-space data sets and determining an intensityvalue for each imaging data frame. Next, an intensity profile is createdand includes a map of the phased array coils designating the intensityvalues of the number of imaging data frames. From the intensity profile,a position of each phased array coil is obtained. The method furtherincludes determining, from the position of each phased array coil, areconstruction data set of imaging data frames from which to form afinal reconstructed image.

[0056] In another embodiment of the present invention, as previouslydescribed, preliminary scanning data is acquired during a fast scan, ora prescan. In this embodiment, the technique is also adaptive anddynamic and does not rely on hardware landmarks, lookup tables, andoperator input parameters for coil/data selection. After initializing afast prescan in acquiring k-space data that includes at least onek-space data line for each of a plurality of MR coils, the techniqueincludes adaptively determining an index gauge for at least one k-spacedata line acquired for each coil. The index gauges are compared to athreshold and based on the comparison, the process can automaticallyselect/deselect a number of MR coils to activate for complete image dataacquisition. By employing a fast prescan, the present invention allowsfor a preliminary analysis to be performed to determine which phasedarray coils are most sensitive to the desired FOV before acquiring afull set of imaging data.

[0057] The step of adaptively determining an index gauge includesextracting a relative intensity of each coil from the acquired k-spacedata, in a manner as previously described. The index gauge can be anintensity value of the k-space data line acquired in the fast prescanfor each coil. In this case, the invention includes arranging theintensity values for the k-space data lines into an intensity profile,selecting a number of phased array coils to activate during final imagedata acquisition from the intensity profile, and acquiring image dataduring the final imaging data acquisition from only the phased arraycoils selected. It is noted that the index gauge can be determinedbefore the image reconstruction because the total intensity is containedin the central portion of the k-space data. Accordingly, the fastprescan is focused at acquiring data in the central portion of thek-space.

[0058] The invention also includes a computer program having a set ofinstructions that, when executed by a computer, causes the computer toanalyze prescan data acquired from activating a number of phased arraycoils during a preliminary MR scan and to extract a relative intensityof each coil from the prescan data. The program then determines a numberof phased array coils to activate in order to acquire reconstructionimaging data during a reconstruction imaging scan from the relativeintensity of each coil.

[0059] In one embodiment, the computer program profiles the relativeintensity for each coil onto a map of a phased array coil assemblyhaving a plurality of phased array coils capable of acquiring theprescan data and activates those phased array coils most sensitive to animaging FOV. Alternatively, the computer program can cause the computerto integrate a coil sensitivity profile weighted by a spin density of ascanning subject over the FOV for each phased array coil to determinethe relative intensity of each coil. The prescan data from a phasedarray coil that is analyzed, includes an intermediate image that can beexpressed in accordance with Eqn. 1, and the relative intensity can beexpressed as an index gauge (G_(i)) according to either Eqns. 2 or 3, orany similar equivalent index gauge that is not dependent upon hardwarelandmarks, operator input parameters, and/or lookup tables. The programalso allows for on-the-fly calculation of a threshold value from therelative intensities to eliminate at least one coil with a lowestrelative intensity.

[0060] Another embodiment of the present invention includes an MRIapparatus to acquire MR images. The MRI apparatus includes a magneticresonance imaging system having a plurality of gradient coils positionedabout the bore of a magnet to impress a polarizing magnetic field and anRF transceiver system. The MRI apparatus further includes an RF switchcontrolled by a pulse module to transmit RF signals to an RF coilassembly to acquire the MR images. The RF coil assembly includesmultiple coils, such as a phased array coil assembly. A computer isprovided and programmed to initialize a fast MR scan using a pluralityof coils in the phased array coil assembly and acquire fast scan imagingdata of a desired FOV. The fast scan imaging data includes at least onek-space line of data for each of the plurality of coils in the phasedarray coil assembly. The computer is further programmed to determine arelative position of each of the plurality of coils with respect to thedesired FOV based only on the at least one k-space line of dataacquired. The computer can then select and initialize a limited numberof coils from the plurality of coils for image acquisition andreconstruction based on the relative positions of each coil in order tooptimize SNR in the desired FOV. The various aforementioned techniquesare used in determining the relative position of each of the pluralityof coils. In this manner, the coils selected more accurately fit the FOVand extraneous data that can have adverse effects on imagereconstruction is not acquired.

[0061] The present invention has been described in terms of thepreferred embodiment, and it is recognized that equivalents,alternatives, and modifications, aside from those expressly stated, arepossible and within the scope of the appending claims.

1. An adaptive method to automatically select/deselect coils in an MRIdevice for improved image reconstruction comprising the steps of:initializing a fast prescan and acquiring k-space data that includes atleast one k-space data line for each of a plurality of MR coils;adaptively determining an index gauge for at least one k-space data lineacquired for each coil; comparing the index gauges; and automaticallyselecting/deselecting, based on the index gauge comparison, a number ofMR coils to activate for image data acquisition.
 2. The method of claim1 wherein the steps of adaptively determining and automaticallyselecting are performed without user input parameters and hardwaremarkers.
 3. The method of claim 1 wherein the adaptively determiningstep is further defined as extracting a relative intensity of each coilfrom the acquired k-space data.
 4. The method of claim 2 wherein the MRcoils are phased array coils and further comprises the steps of:selecting a desired FOV; determining a relative position of each phasedarray coil with respect to the desired FOV; and activating the phasedarray coils most sensitive in the desired FOV.
 5. The method of claim 1wherein the MR coils are phased array coils and wherein the index gaugeis an intensity value of at least one k-space data line acquired in thefast prescan for each coil, and further comprises: arranging theintensity values for the k-space data lines into an intensity profile;selecting a number of phased array coils to activate during final imagedata acquisition from the intensity profile; and acquiring imaging dataduring the final imaging data acquisition from only the phased arraycoils selected.
 6. The method of claim 1 wherein the index gauge isdetermined by finding a total intensity of each image, which isproportional to, and found by, integrating a coil sensitivity profileweighted by a spin density of a scanning object over a desired FOV. 7.The method of claim 1 wherein the step of adaptively determining anindex gauge further comprises the step of determining a coil positionexplicitly.
 8. The method of claim 7 wherein the step of determiningcoil position explicitly, includes determining whether any coil ispositioned at least partially outside a desired FOV relative topositions of a number of coils within the desired FOV.
 9. The method ofclaim 7 wherein the coil position is determined by one of: projecting anintensity of the k-space data onto an axis of the MR coils andconducting a profile fit; calculating a center of mass of an intensityprofile; and determining a peak location of the intensity profile alongan axis of the MR coils.
 10. The method of claim 1 wherein the step ofinitializing a fast prescan and acquiring k-space data includesobtaining only a central portion of k-space data to determine a totalintensity of each image as the index gauge.
 11. The method of claim 1wherein the index gauge (G_(i)) is determined by approximating aconstant spin density according to:${G_{i} = {\sum\limits_{({x,y})}\left| {{S_{i}\left( {x,y} \right)}{M\left( {x,y} \right)}} \middle| {\approx {M\quad o\sum\limits_{({x,y})}}} \middle| {S_{i}\left( {x,y} \right)} \right|}},$

where S_(i)(x,y) is a spatial sensitivity of an i-th MR coil of anN-coil phased coil array, and M(x,y) is a spin magnetization densityweighted by an imaging sequence, M_(o) is the approximated constant spindensity, and where the summation is over all spatial pixels in a desiredFOV.
 12. The method of claim 1 wherein the index gauge (G_(i)) isdetermined without assuming a constant spin density according to:$G_{i} = {{\sum\limits_{({x,y})}\left( \left| {I_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {I_{i}\left( {x,y} \right)} \right| \right)} = {\sum\limits_{({x,y})}\left( \left| {S_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {S_{i}\left( {x,y} \right)} \right| \right)}}$

where S_(i)(x,y) is a spatial sensitivity of an i-th MR coil of anN-coil phased coil array, I_(i)(x,y) is a total intensity obtained fromcentral k-space data for each MR coil, and wherein the summation is overall spatial pixels in a desired FOV.
 13. The method of claim 1 whereinthe step of comparing includes determining a threshold on-the-fly forevaluating the data acquired from each coil and eliminating a coil witha least SNR, wherein the threshold is determined based only on the indexgauges for each of the coils.
 14. A computer program having a set ofinstructions that when executed by a computer causes the computer to:analyze prescan data acquired from activating a number of phased arraycoils during a preliminary MR scan; extract a relative intensity of eachcoil from the prescan data; and determine, from the relative intensityof each coil, a number of phased array coils to activate to acquirereconstruction imaging data during a reconstruction imaging scan. 15.The computer program of claim 14 wherein the determination act includeson-the-fly calculation of a threshold value from the relative intensityof each coil to eliminate at least one coil with a lowest relativeintensity.
 16. The computer program of claim 14 wherein the set ofinstructions further causes the computer to: profile the relativeintensity for each coil onto a map of a phased array coil assemblyhaving a plurality of phased array coils capable of acquiring theprescan data; and activate those phased array coils most sensitive to animaging FOV.
 17. The computer program of claim 14 wherein the set ofinstructions further causes the computer to activate for imagereconstruction those phased array coils that produce a relativeintensity having a value greater or equal to an intensity thresholdvalue.
 18. The computer program of claim 17 wherein the intensitythreshold value includes a mean of the data frame intensity values. 19.The computer program of claim 14 wherein the set of instructions furthercauses the computer to integrate a coil sensitivity profile weighted bya spin density of a scanning subject over a field-of-view for eachphased array coil to determine the relative intensity of each coil. 20.The computer program of claim 14 wherein the prescan data from a phasedarray coil includes an intermediate image which is represented by: I_(i)(x,y)=S _(i)(x,y)M(x,y) where: I_(i)(x,y) is the prescan data of ani-th phased array coil; S_(i)(x,y) represents a spatial sensitivity ofthe i-th phased array coil; and M(x,y) represents a spin density of ascanning subject within a desired field-of-view.
 21. The computerprogram of claim 20 wherein the relative intensity is represented as anindex gauge (G_(i)) and is determined by: approximating a constant spindensity according to:${G_{i} = {\sum\limits_{({x,y})}\left| {{S_{i}\left( {x,y} \right)}{M\left( {x,y} \right)}} \middle| {\approx {M\quad o\sum\limits_{({x,y})}}} \middle| {S_{i}\left( {x,y} \right)} \right|}},$

where S_(i)(x,y) is a spatial sensitivity of an i-th MR coil of anN-coil phased coil array, and M(x,y) is a spin magnetization densityweighted by an imaging sequence, M_(o) is the approximated constant spindensity, and where the summation is over all spatial pixels in a desiredFOV.
 22. The computer program of claim 20 wherein the relative intensityis represented as an index gauge (G_(i)) and is determined by withoutassuming a constant spin density according to:$G_{i} = {{\sum\limits_{({x,y})}\left( \left| {I_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {I_{i}\left( {x,y} \right)} \right| \right)} = {\sum\limits_{({x,y})}\left( \left| {S_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {S_{i}\left( {x,y} \right)} \right| \right)}}$

where S_(i)(x,y) is a spatial sensitivity of an i-th MR coil of anN-coil phased coil array, I_(i)(x,y) is a total intensity obtained fromcentral k-space data for each MR coil, and wherein the summation is overall spatial pixels in a desired FOV.
 23. The computer program of claim14 wherein the relative intensity is extracted by the computer programaccording to one of: projecting an intensity of the k-space data onto anaxis of the MR coils and conducting a profile fit; calculating a centerof mass of an intensity profile; and determining a peak location of theintensity profile along an axis of the MR coils.
 24. An MRI apparatuscomprising: a magnetic resonance imaging (MRI) system having a pluralityof gradient coils positioned about a bore of a magnet to impress apolarizing magnetic field and an RF transceiver system and an RF switchcontrolled by a pulse module to transmit RF signals to a phased arraycoil assembly to acquire MR images; and a computer programmed to:initialize a fast MR scan using a plurality of coils in the phased arraycoil assembly; acquire fast scan imaging data of a desired FOV whereinthe fast scan imaging data includes at least one k-space line of datafor each of the plurality of coils in the phased array coil assembly;determine a relative position of each of the plurality of coils withrespect to the desired FOV based only on the at least one k-space lineof data; and select and initialize only a number of coils from theplurality of coils for image acquisition and reconstruction based on therelative positions of each coil to optimize SNR in the desired FOV. 25.The MRI apparatus of claim 24 wherein the computer is further programmedto: determine an intensity value for at least one k-space line of datafor each of the plurality of coils; determine a coil sensitivity valuefor each of the plurality of coils from the intensity value of eachk-space line of data; and determine coil position relative to thedesired FOV from the coil sensitivity values.
 26. The MRI apparatus ofclaim 25 wherein the computer is further programmed to reject at leastsensitive coil in the desired FOV for image reconstruction.
 27. The MRIapparatus of claim 25 wherein the computer is further programmed to:identify coils most sensitive to the desired FOV by comparing asensitivity value for each coil to a sensitivity threshold value, and toselect only the coils that have sensitivity values that are equal to orgreater than the sensitivity threshold value for image data acquisition.28. The MRI apparatus of claim 25 wherein the computer is furtherprogrammed to: create an intensity profile that includes a projection ofeach intensity value onto a map of the plurality of coils; and determinea center of mass of the intensity profile to locate a relative positionof each coil. 29.The MRI apparatus of claim 24 wherein the computer isfurther programmed to calculate an index gauge (G_(i)) to adaptivelydetermine the relative position of the plurality of coils.
 30. The MRIapparatus of claim 29 wherein the computer is further programmed tocalculate the index gauge (G_(i)) according to one of: by approximatinga constant spin density according to:${G_{i} = {\sum\limits_{({x,y})}\left| {{S_{i}\left( {x,y} \right)}{M\left( {x,y} \right)}} \middle| {\approx {M\quad o\sum\limits_{({x,y})}}} \middle| {S_{i}\left( {x,y} \right)} \right|}},$

where S_(i)(x,y) is a spatial sensitivity of an i-th MR coil of anN-coil phased coil array, and M(x,y) is a spin magnetization densityweighted by an imaging sequence, M_(o) is the approximated constant spindensity, and where the summation is over all spatial pixels in a desiredFOV; and$G_{i} = {{\sum\limits_{({x,y})}\left( \left| {I_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {I_{i}\left( {x,y} \right)} \right| \right)} = {\sum\limits_{({x,y})}\left( \left| {S_{i}\left( {x,y} \right)} \middle| {/\sum\limits_{i}} \middle| {S_{i}\left( {x,y} \right)} \right| \right)}}$

where S_(i)(x,y) is a spatial sensitivity of an i-th MR coil of anN-coil phased coil array, I_(i)(x,y) is a total intensity obtained fromcentral k-space data for each MR coil, and wherein the summation is overall spatial pixels in a desired FOV.
 31. The MRI apparatus of claim 25wherein the computer is programmed to determine a relative position ofeach of the plurality of coils on-the-fly and without a lookup table byfinding a total mean value of an index gauge for each coil.
 32. An MRIdevice for improved image reconstruction comprising: means forinitializing a fast prescan and acquiring k-space data that includes atleast one k-space data line for each of a plurality of MR coils; meansfor determining an index gauge for at least one k-space data lineacquired for each coil; means for comparing the index gaugesdynamically; and means for automatically selecting/deselecting a numberof MR coils to activate for image data acquisition based on thecomparison.